The present invention relates to a load cell that transmits and measures linear forces along and moments about three orthogonal axes. More particularly, a compact load cell body is disclosed having a rigid central hub, a rigid annular ring concentric with the hub and radial members extending between the central hub and the annular ring. The load cell body has improved performance and characteristics of which can be easily adjusted to vary the sensitivity of the load cell.
Transducers or load cells for determining forces along and moments about three orthogonal axes are known. Two such load cells are disclosed in U.S. Pat. Nos. 4,640,138 and 4,821,582. U.S. Pat. No. 4,640,138 illustrates a multiple axis load-sensitive transducer having inner and outer members that are joined by a pair of axially spaced spiders. The spiders comprise arms that are integral with the inner member and are connected to the outer member by flexible straps that have longitudinal lengths with the ends of the straps fixed to the outer member. The arms of the spiders are fixed to the center of the associated strap. Loads are sensed as a function of bending on the spider arms.
U.S. Pat. No. 4,821,582 illustrates a load transducer that measures linear forces in three axes and moments about two of the axes. The transducer has inner and outer structures connected by load-sensitive spider arms or shear beams. The outer ends of the spider are connected to outer lengths which are stiff when the inner structure is loaded in a direction along an axis perpendicular to the plane of the spider.
Other, more compact, load cells are described in United Kingdom Patent Application GB 2096777 A. These load cells include a central hub portion and an annular ring portion with four radial spoke portions connecting the hub and ring portions and having suitable strain gauges adhered thereon. A prior art load cell having this construction is discussed in GB 2096777 A but does not measure moments applied about axes extending through the spokes. United Kingdom patent application GB 2096777 A discloses solid spokes having trunk sections and end sections. Each end section has a "width" dimension that is less than the corresponding trunk section. The reduced width of each end section is sufficiently small to make it flexible with respect to a twisting force about the extending direction of the spoke.
There is an ongoing need to provide an improved compact load cell, which is easy to manufacture and measures components of force and moment in plural directions.